Inductive power transfer (IPT) or inductively coupled power transfer (ICPT) systems are well known and used for a number of industrial applications, and have particular advantages where traditional methods are unable to perform satisfactorily, for example clean rooms, people moving, materials handling, battery charging, or any application requiring a substantially contactless supply of power.
A typical IPT system consists of three main components; an AC power supply, a primary conductive path, and one or more electrically isolated pickups coupled with a load and provided substantially adjacent the primary conductive path. Together, the power supply and primary conductive path form the primary side of an inductive power transfer system, while the pickup(s) and associated circuitry forms the secondary side.
The primary conductive path, typically in the form of an elongated conductive loop or track, is energised by the AC power supply to create a continuously varying magnetic field about the track. The or each pickup includes an inductive coil, in which a voltage is induced by the changing magnetic flux passing through the coil in accordance with Faraday's law of induction, thereby achieving contactless inductive power transfer.
Typically, the pickup will include some form of controller circuit to control the transfer of power to the load, including a switched-mode controller such as a boost converter, for example, to supply the relatively constant output voltage required by the load.
The power supply will commonly also be provided with a power controller. In single pickup systems, the power controller may be adapted to reduce the track current in the primary conductive path to reduce power and minimise losses at partial loads, and/or to increase the track current to compensate for a weak magnetic or inductive coupling when the pickup coil is not ideally aligned with the primary conductive path, for example, to ensure the required power is supplied to the load. In multiple pickup systems, the power controller will usually be adapted to maintain a constant current in the primary conductive path or track, to ensure that all pickups are adequately powered.
In some applications, it can be advantageous or desirable to enable contactless bi-directional power flow between the primary and secondary sides of the system. Bi-directional power flow has a number of potential applications in IPT systems, such as returning excess power generated or stored by a ‘load’ coupled with a pickup to the electricity supply grid. Presently, there is no known IPT system, or more particularly no known power controller for an IPT system, which facilitates bi-directional power flow in a single system. This is desirable for a number of reasons, including reducing costs, simplicity for diagnosis and repair, and improved efficiency due to the ability to re-generate and return power to the grid, for example.